The airways, extending from the nares to the alveoli, have a complex geometry and function. Their size, shape, and consequently resistance to airflow is influenced by numerous factors, including changes in neuronal drive to the upper airway dilating and constricting muscles, airway smooth muscles and airway vasculature. During sleep, activity of the upper airway dilating muscles is reduced and cholinergic outflow to airway smooth muscle is increased. This leads not uncommonly to sleep obstructive apnea and worsening of the airway functions. Neuroanatomical projections, neurotransmitters and signaling pathways mediating sleep-related changes are not well understood. This proposal consists of research focused on the central networks involved in regulation of breathing and airway patency during sleep. The first part deals with 1) the neurochemical organization and axonal projections of the CNS cell groups that are activated during sleep, 2) identification of the target neurons of the sleep promoting sites and their relation to hypoglossal and airway related vagal preganglionic neurons, and the second part with 3) the neurochemical organization of neurons that mediate sleep-related modulations of the automatic functions and motor activities of upper airway dilating and constricting muscles. Fos expression will be used to identify neurons activated during sleep, to investigated the basic chemical neuroanatomy of these cells, to co- localized putative neurotransmitters in sleep activated neurons, and to determine pathways and connections between these structures and the hypoglossal and airway related-vagal preganglionic neurons. The data derived from these studies will provide basic information related to central networks, neurochemical organization, and chemical nature of communications between sleep promoting cells and brainstem output neurons. The results will have a direct bearing on our understanding of neurochemical mechanisms underlying centrally mediated respiratory and airway functions during sleep, such as obstructive sleep apnea and the nocturnal worsening of asthma.